Determination of habitual physical activity by means of a portable R-R interval distribution recorder.

A new portable apparatus-the Interval Distribution Recorder (IDR)-has been developed by WHO for assessing habitual physical activity. It measures R-R intervals and records counts in 8 heart rate classes-i.e., at 8 levels of physical activity, from sleeping to heavy exercise. It is much simpler, easier to operate, and less expensive than tape recording systems, and it requires only a minimum of skill and of cooperation by the unsupervised subject. It is therefore suitable for population studies. The IDR system yields more precise information than that obtained by using heartbeat totalizers, which only give a mean heart rate value for the day and do not allow detection of differences in activity patterns.